Method of distilling heavy lubricating oils



Feb. 19, 1935. e. B. COUBROUGH 1,991,791

METHOD OF DISTILLING HEAVY LUBRICATING OILS Filed March 20, 1933 DILUENTGAS OIL I 46 .3@\ 1zV: L .36)

WAX DISTILLATE CYLINDER STOCK ASPHALT tacted with the descending reflux.As a conse- Patented Feb. 19, 1935 UNITED, STATES METHOD OF DISTILLINGHEAVY LUBRICATING OILS George B. Coubrough, Long Beach, Calif., as-

signor to The Lummus Company, New York, N. Y., a corporation of DelawareApplication March 20, 1933, Serial No. 661,728

2 Claims.

The present invention relates to methods of distilling heavy lubricatingoils and more particularly to improvements in the method described in my,Patent No. 1,905,156, dated April 25, 1933.

The method described in my patent consists in fractionating a reducedcrude by a primary distillation to obtain a residue consisting of heavylubricating oils and asphalt, mixing the residue 'with a light diluentsuch as kerosene or gas oil, and flash vaporizing the diluent and thelubricating oil together as a unit from. the asphalt in a vacuum column.The'flash'vapors are then rectified or fractionally condensed toseparate the diluent from the lubricating oils. J

As explained in the patent, the final column is preferablynot calledupon to effect any rectification between adjacent fractions andaccordingly, the heaviest lubricating fraction is determined in itscharacteristics by the cut in the primary column. That is to say, ifcylinder stock containing only the heaviest lubricating oil componentsof the crude is desired, substantially allof the lighter constituentsshould be removed in the primary column.

However, in view of the overlapping characteristics of the components ofthe crude, a small quantity of undesirable oils may find their way intothe final column. These undesirable oils which may be termedintermediates, may result from a failure to attain a perfect separationin the primary column or from a slight decomposition in the finalheating stage. The intermediates, although small in quantity, wouldlower the flash point of the cylinder stock if permitted to collecttherein. If not permitted to collect in the cylinder stock, they wouldpass overhead with the diluent and eventually would so build up in thediluent as to prevent-further use thereof in the process.

According to the present invention, the diluent and cylinder stock areseparated by rectification in thefinal column and "the intermediates arecaused to collect in a portion of the rectifying section from which theyare continuously bled. In the preferred form of the invention, thecylinder stock is subjected to a side stripping operation to remove anyremnant of light and intermediate oils and the vapors thus evolved areconquence, the undesired intermediates being subjected to vaporizationfrom below and to condensation from above tend to concentrate in thelower decks'of the rectifying section from which they are continuouslywithdrawn so that they have no opportunity to build up in the column.

divided into three products, namely, a gas oil The material bl'ed oflcomprises only a small percentage of the total amount of liquid handled.As a further feature of the invention, this material maybe returned tothe primary column for segregation of any valuable constituents it may 5contain. As stated in my patent, it is undesirable to attemptrectification over a large number of decks because of the back pressurein the vaporizing zone. According to the present invention, only a fewdecks are required, since any incompleteness of separation between thelubricating oil and the diluent is taken care of by the bleeding of asmall quantity of liquid from the rectifying section. Consequently, theheavy lubricating stock may be manufactured to substantially any desiredspecifications of viscosity and flash point and the diluent may berecovered in substantially Y its original form suitable for re-use inthe process or forany other purpose.

The accompanying drawing is a diagram of the preferred form of apparatusfor practising the present invention.

The reduced crude from which the lighter materials such as gasoline,kerosene, and part of the gas oil have been removed is continuouslypumped through a pipe heater 2 into the vaporizing zone of a primarycolumn 4. Steam is introduced at. ,6 below the point of feed. In thiscolumn, the oil overhead, a wax distillate side product, anda residuecontaining the remainder of the lubricating oils (cylinder stock) andasphalt. According- 1 ly, the column isprovided with a rectifyingsection 8 above the feed, an upper rectifying section 10, and ,a sidestripping section 12, all of which are provided with contact decks ofany suitable form. The gas oil is condensed in a condenser 14 and afterit is decanted from the water, a part is returned through the pipe 16 asreflux, the remainder being withdrawn as a product. Stripped waxdistillate is drawn off the stripping section at 18. A slop draw-01f 20is provided at one or more decks of the rectifying section 8. for apurpose later to be described. a

In the column}, a closeseparation is made between the wax distillate andthe cylinder stock so that the residue contains substantially onlyasphalt and cylinder stock of specified initial boiling point. Asexplained in my patent above referred to, the division between thelubricating oils is made in the primary distillation in order that thefinal vaporizing column may not be required to perform the duty ofrectifying between the cylinder stock and any substantial amount ofadjacent lighter components. The residue is Withdrawn from the column 4by a pipe 21 and is mixed with diluent introduced by the pipe 22, thisdiluent being preferably a kerosene of narrow boiling range. The entiremixture is forced by a pump 24 through a pipe heater '26 into a finalcolumn 28, preferably at a temperature of about 700 F. In the column 28,all of the oils including thelubricating stock and diluent are flashedas a unit under the contained heat of the mixture, the vaporizationbeing enhanced by maintenance of a vacuum and also by the use of steamintroduced at 30. Above the point of feed, the column is provided withentrainment catching decks 32, and a rectifying section 34 wherein theseparation of the cylinder stock from the diluent takes place. At thebottom of the rectifying section 34 is a steam stripping section 36 intowhich steam is introduced at 38 for the purpose of removing any remnantof diluent from the cylinder stock. The cylinder stock is drawn off thestripping section at 40. The diluent is condensed overhead in acondenser 42 to which any suitable vacuum pump or jet is connected. Thecondensed diluent is separated from the water, a part being withdrawn at44, and the remainder being returned to the column as reflux through apipe 46. The diluent withdrawn at 44 may be returned directly to thepipe 22, and

thereby continuously recirculated in the system, but due to unavoidableloss, a small make-up is necessary and accordingly, it is preferred torun the pipe 44 to a storage tank from which it may be withdrawn asneeded.

The mixture introduced into the column 28 may contain some intermediatecomponents which are not desired in the lubricating stock. Theseundesirable materials may consist of a small amount of wax distillatewhich has not been completely removed in the primary column 4, orpossibly of a small amount of material decomposed in the heater 26. Inany event, they are components which would lower the viscosity of thecylinder stock. Furthermore, since they are being continuouslyintroduced into the final column 28, they are equally undesirable in thediluent. If removed from the cylinder stock, they tend to concentrate inthe diluent and if the diluent is continuously recycled, it eventuallywould become so contaminated as to be useless. It will be appreciatedfurther that even if the diluent obtained at 44 is not continuouslyrecycled, the presence of'these intermediates would materially reducethe commercial value of the diluent.

Inasmuch as the undesired intermediates are being continuously removedfrom the cylinder stock in the stripping section 36, they tend to risethrough the rectifying zone 34. At the same time, the descending refluxof diluent tends to force the intermediates down through the rectifyingzone. As a consequence, they are found in greatest concentration on thelower decks of the rectifying zone. I 1

According to the present invention, a small quantity of liquid on thelower decks of the rectifying zone is continuously bled off by bleedpipes illustrated at 46. The quantity of material thus 'bled off ispreferably about'5 to 10% of the total quantity of diluent. Thismaterial comprises largely diluent with possibly a small amount ofcylinder stock, contaminated with the undesired intermediate products,which have concentrated on the lower decks. As a result of thecontinuous bleeding of the rectifying zone, the intermediates are notpermitted to build up in the column and are therefore removed from thezone of reaction before they have an opportunity either to pass upwardlyinto the diluent or downwardly into the stripping section.

The material bled at 46 may be thrown away without great loss, since itis small in quantity as compared to the total volume of diluent.However, since it contains values in the form of diluent as well ascylinder stock, it is preferably returned through a pipe 48 into thefeed line which runs to the primary column 4. By mixing with theoriginal feed, the components associate themselves with correspondingcomponents of the feed and ultimately find their proper places either inthe overhead, the side product, or the residue. Any intermediatematerials which are undesirable either in the cylinder stock or the waxdistillate may be suppressed into the rectifying section 8 andultimately find their way to the slop draw-oil 20.

According to the present process, the cylinder stock can be manufacturedto any desired specifications of gravity and viscosity, and the diluentmay be recovered in form suitable for continuous recirculation in theprocess. Although it has been stated in my prior patent that a closeseparation between the cylinder stock and the diluent may be dimcult toattain by ordinary methods, it will be understood that the bleeding ofintermediates at 46 materially improves this separation and insuresagainst the presence of any diluent in the cylinder stock or of anycylinder stock in the overhead diluent.

Having thus described the invention, .what is claimed is:

i 1. The method of dividing a reduced crude which consists in subjectingthe reduced crude to a primary distilling operation to leave a residueconsisting of lubricating oils of a substantially predetermined initialboiling point in mixture with asphalt, mixing said residue with adiluent of materially lower boiling point, heating the entire mixtureand introducing it into a vaporizing zone to vaporize the lubricatingoils and the diluent as a unit, passing the vapors into a rectifyingzone to contact with a descending reflux of diluent whereby lubricatingstock is condensed. continuously bleeding from the rectifying zone asmall quantity of reflux containing imperfectly separated lubricatingoil and diluent components and returning said bled material to theprimary" distilling operation.

2. The method of dividing a reduced crude which consists in subjectingthe reduced crude to a primary distilling operation to leave a residueconsisting of lubricating oils of a substantially predetermined initialboiling point in mixrectifying zone to contact with a descending refluxof diluent whereby lubricating stock is condensed, stripping thelubricating stock with steam to vaporize any light and intermediatecomponents therefrom, bleeding from the rectifying zone a small quantityof material, and re-' turning said bled material to theprimarydlstilling operation.

GEORGE B. COUBROUGH.

